The present invention relates generally to vehicle towed trailers. More specifically, the present invention relates to a method and apparatus to detect trailer instability in a vehicle-trailer configuration or arrangement and compensate for the trailer instability.
Towing trailers behind a vehicle is a common practice for today""s vehicle owners. Typically, a vehicle such as a truck will be equipped with a trailer hitch that may be coupled to numerous types of devices such as a trailer. The vehicle will have to provide sufficient engine torque and directional stability to pull the trailer. A trailer may become unstable when it is improperly loaded or there are tire pressure differences in the trailer wheels. Improper trailer loading generally occurs when there is a failure to equally distribute the trailer""s cargo over the left and right sides of the trailer. Once the tow vehicle and trailer are in motion, an improperly loaded trailer may become unstable and generate oscillations that may propagate to the vehicle towing the trailer. Furthermore, other environmental factors may induce instability in a tow vehicle and trailer arrangement including crosswinds, road conditions, driving maneuvers, and other similar conditions.
Presently, trucks may include four-wheel steering or steering of all four tires of a vehicle. The steering of a rear axle or wheels is accomplished through the use of an electric motor driving a rear steering rack. Through electronic controls from a controller in the vehicle, the electric motor controlling the rear steering rack may turn the direction and angle of the rear wheel tires as a function of the front wheel steering or as functions of other environmental factors. Four-wheel steering may be used to stabilize a vehicle affected by numerous driving conditions.
The present invention includes a method and apparatus to compensate for instabilities generated by a trailer towed by a vehicle. The present invention utilizes sensors to detect the onset of instabilities in a vehicle and trailer tow arrangement such as oscillations and corrects these instabilities using the four-wheel steering system on a vehicle. The corrections by the four-wheel steering system may compensate for the disturbances in their infancy by detecting the disturbances before they affect the performance of the vehicle-trailer tow arrangement.
By effectively detecting the articulation angle of the trailer, algorithms may characterize the oscillation. If the oscillation is characterized as presenting an unstable driving condition, four-wheel steering can be utilized to cancel the onset of trailer instability. Cancellation of trailer oscillations will prevent the oscillations from affecting vehicle yaw and ride quality as well as preventing potentially dangerous driving situations.
The sensors used by the present invention include, but are not limited to, strain gauges, liner potentiometers, linear encoders, limit switches, infrared detectors, ultrasonic sensors, and optical cameras. The sensors used in the present invention initiate compensation for a trailer load imbalance by detecting an oscillation in the trailer dynamics. An important function of the invention is to detect the trailer instability at the onset of the trailer oscillations.
Unstable trailering conditions generally occur when three or four oscillations with a delta of zero to five degrees occur in less than two seconds. By detecting the trailer angle deltas, algorithms will be utilized to characterize the oscillation and command the appropriate four-wheel steering actuation. The specific algorithms employed may be vehicle specific and are not limited by the described criteria. The characteristics of trailer instability are dependant on the specific tow vehicle and trailer combination.